The thin tissue forming the outer layer of a body 's surface and lining the alimentary canal and other hollow structures is the epithelium.

Membranous tissue composed of one or more layers of cells separated by very little intercellular substance and forming the covering of most internal and external surfaces of the body and its organs are epithelial. i.e, Epithelial means of or belonging to epithelium.

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epithilal an animal tissue consisting of one or more layers of closely packed cells covering the external and internal surfaces of the body. The cells vary in structure according to their function, which may be protective, secretory, or absorptive

Characteristics of epithelial tissue:

Epithelial tissue lies on a basement membrane. That means that underlying the cells that are the cellular component of the epithelial tissue, there is a layer of acellular ("a-" means not, so "acellular" means not cellular) material. This basement membrane can be thought of as a sticky layer to keep the epithelial cells attached to whatever underlies them. The bottom edge of the epithelial tissue abuts the basement membrane; this bottom edge is called the basal surface. The edge of the epithelial tissue that faces the lumen (or the outside world) is called the apical surface.

Other characteristics:

Cells within this tissue readily divide to make more cells. This helps this tissue recover after any sort of abrasions occur.

This tissue does not have any vasculature. This means that there are no blood vessels within it. This should make sense, since epithelial tissue is likely to get damaged by material moving against it-- and you don 't want to bleed everytime something bangs into your skin or everytime you swallow something rough.

The cells within this tissue are firmly attached to each other. As a border-tissue, if the cells weren 't adherent to one another, it would be a leaky border. This would be no good-- liquids from inside of us would drip out! Yuck! So the cells all make the type of junctions with each other calledtight junctions.